Ancient air bubbles could revise history of Earth’s oxygen

If new findings are correct, rise in gas preceded earliest animals

NOT-SO-FRESH AIR Ancient air embedded inside rock salt for 815 million years suggests that oxygen was already abundant when the first animals appeared. The microscopic air bubbles were trapped inside rectangular inclusions (one circled in red) in the rock.

Chris Lecuyer

Whiffs of ancient air trapped in rock salt for hundreds of millions of years are shaking up the history of oxygen and life on Earth.

By carefully crushing rock salt, researchers have measured the chemical makeup of air pockets embedded inside the rock. This new technique reveals that oxygen made up 10.9 percent of Earth’s atmosphere around 815 million years ago. Scientists have thought that oxygen levels would not be that high until 100 million to 200 million years later. The measurements place elevated oxygen levels well before the appearance of animals in the fossil record around 650 million years ago, the researchers report in the August issue of Geology.

“I think our results will take people by surprise,” says study coauthor Nigel Blamey, a geochemist at Brock University in St. Catharines, Canada. “We came out of left field, and I think some

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